Summary

In Switzerland, transplants for organic vegetable growing have been fertilised traditionally with slaughterhouse by-products. In autumn 2000, the Swiss government restricted the use of such products because of the BSE crisis. To maintain the production of organic transplants, alternative fertilisers needed to be tested. Eleven alternatives to horn powder (standard fertiliser) were selected based on the organic standards of the European Union, including feather powder (as an animal based product without BSE risk). The products were mixed with a standard growing media for organic transplants in a concentration of 300 mg nitrogen L-1 growing media. Different experiments where set up with head lettuce (Lactuca sativa), Chinese cabbage (Brassica rapa var. pekinensis) and fennel (Foeniculum vulgare), at two different planting times: immediately after mixing the growing media and six weeks after mixing, in heated and cold greenhouses. Beside weight per plant, we assessed phytotoxic effects 0, 2, 4 and 6 weeks after mixing the media, and mineralised nitrogen in the growing media. When planting immediately after mixing, potato protein, vinasse (wastes of food processing), and feather powder resulted in the highest weight per plant. Plants fertilised with horn powder, sunflower oil cake and ground field beans had the lowest weight per plant (40% less). Horn powder, ground malt sprouts, vinasse, potato protein and feather powder with stored growing media produced the strongest transplants. Phytotoxicity tests (four different methods) showed significant differences between horn powder (slight damage) and field beans (seriously harmed). Horn powder is still the best fertiliser for organic transplant production followed by feather powder. Horn powder causes little phytotoxicity to the crop even under extreme conditions. The most promising pure plant products are potato protein, malt sprouts and vinasse. Plant-based fertilisers need to be applied carefully; the fertiliser should be mixed with the growing media at least two weeks before sowing.